John a



(No Model.)

J. A. BARRETT.

TELEPHONE GIRGUIT.

No. 350,715. Patented Oct. 12, v1886.

@El N i\\%| l l P5: r` @l ne: l l l l l l l l lil llIIIIl lll llllll l lll ll lllll lll'llllll'm Wneemy@ @me UNITED STATES PATENT OFFICE.

JOHN A. BARRETT, OF BROOKLYN, ASSIGNOR TO THE AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, OF NEV YORK, N. Y.

TELEPHONE-CIRCUIT.

SPECIFICATION forming part of Letters Patent No. 350.715. dated October 12, 1886.

A pplieation tiled July 19, 1986.

To all whom t may concern:

Be it known that I, JOHN A. BARRETT, residing at Brooklyn, in the .county of Kings and State of New York, have invented certain Improvements in Telephone-Ciieuits, of which the following is a specification.

This invention is an improvement in telephone circuits and apparatus, whereby I am enabled to avail myself of the immunity from inductive disturbance inherent in the use ot' a parallel metallic return-circuit, retaining at the saine time the ability to transmit two simultaneous messages over the said metallic circuit in either direction, so that, although the cost of one metallic circuit includes that of two complete wires, the additional outlay is substantially neutralized by the ability to send two messages simultaneously over the said metallic circuit, but one, however, of these commu uieations participates in the benefits of the metallic circuit.

Furthermore, the principle of the invention is not restricted to a single metallic circuit, but may be carried out to an indefinite extent, as hereinafter described. lt is well-known that when two electrical cond actors are placed in proximity variations of the electrical condition of one will develop inductive electri cal currents in the other more or less accentuated, according to the character of the initial variations and degree of proximity of the two conductors in question. This phenomenon. is very pronounced in the case of telephone-circuits, which, by reason of the extreme seusitiveness ot' the receiving-instru ment, are oftentimes greatly troubled by ad verse currents induced by parallel telcgraphie or telephonie circuits, which act both to confuse and drown out the desired sounds, and also to reproduce upon any individual telephonie circuit .messages which are passing upon the other lines. A well-known expedient frequently adopted to neutralize these ad verse influences is to substitute a returirwire for the ordinary grou]itl-terminals or groundretnrn ot' the telephone-circuit. This p1an,to give satisfaction, requires that both direct and return wire must be substantially equidistant from the source or sources ot' disturbance. The chietl disadvantage which this plan pre- Sents is the greatly-increased cost, which, it is Serial No. 208,463. (No model.)

evident, is nearly double that ol" a single-line circuit or system of circuits. For this reason it has proved very desirable that some mode or arrangement ot' circuitsshould be obtained whereby the advantages ol' the metallic eircuit should be retained, and wherebyits ehiet` disadvantage recited above, should be materially curtailed.

To provide such an arrangement of circuits and apparatus is the main object of my invcntion. Heretotbre and prior to my invention the only way devised l'or the attainment of this object has been to connect the metallic circuit transmitiiugand receiving instruments in the bridge-wire of :t Yilheatstoues bridge arrangement ot' circuits, effecting a balance by suitably-proportioned resistanccs included in the two branches between the said bridgewire and the union ol" the direct and return wires, and by including-a second set of telcgraphic or telephonie instruments in earth branches at both ends ofthe circuit. In this arrangement the two earthbranch instruments work respondently, the bridgewire instruments also being adjusted to work with one another only, and being irresponsive to the action of the earth-branch instruments. This principle ot' operation is capable of considerable extension. in practice. For example,the two wires of two distinct metallic circuits may be utilized as the direct and return conductors ot' a compound metallic circuit having instruments in a bridge-wire, in which case the earth branch would be extended from the junction-point of the two metallic circuits, and such a system may be indefinitely carried out.

So far as am aware, Letters Patent of the United States No. 287,288, issued October 23, '1.883, to Frank Jacob, fully exemplify the state of the art embodying the principle ofoperation hereinbefore described.

My invention is an improvement inthe said art and in the appliances required in Operating the same. Experience has demonstrated that the di rect-operating-l)ridge arrangement has certain defects which by my invention are overcome. A considerable portion ef the energy of the current traversing the circuit is dissipated or transformed in the circuit itself in overcoming the balancing-resistances, and the operating-current is necessarily so subdi- ICO vided that its action upon the receiving-magnets is of an extremely limited nature.

My invention, broadly stated, consists in bringing the metallic ordouble-wire instruments at the terminal stations into inductive relation by means of converting or repeating induction-coils with both sides of the circuit, instead of connecting them directly with the said circuit by means of a bridge-wire. The currents traversing the metallic circuit are thus economized, inasmuch as they are only required to traversea direct circuit, while the accompanying currents, which are initiated in the earth branch at either terminal station to actuate the corresponding receivinginstrument in the distant earth branch, cannot affect` the intermediate double-wire instruments, as the current generated by the said earth-branch transmitters at any given instant acts upon.

both sides of the doub1e-wire receivers alike, the current induced in one converting-coil being opposite in direction to that induced in the other at the same instant,so that its effect is thus neutralized by its own action.

I provide a double-wireline circuit, and at the terminal stations I'include in each wire of the circuit an induction-coil preferably wound with two insulated wires side by side, lone of which wires is directly in circuit with the dou ble-wire line, while the other is connected in circuit with the secondary helix of atelephone` transmitter and with the coil of a telephonereceiver. Thus messages from a distant station reach the receiver by means of induction through the converting-coils, one of which is in the direct and the other in the return wire, while messages lspoken in the transmitter develop currents in the secondary circuit of the induction coil thereof, and these again by induction develop tertiary currents ofcoincident direction with one another in both convertingcoils simultaneously, which currents, being of like direction, re enforce one another and traverse the line to act through like converters upon the distant receiver. To a point of the metallic circuit at each terminal station, substantially cquidistant from the convertingcoils, I attach an earth branch, including the usualtelephone-instruments. Telephonie currents developed in the transmitters at either terminal station in the earth branches will traverse both direct and return wire in the same direction-that is, in relation to any intermediate point or appliance the current in both lines will be at any given moment positive or negative; hence, while the receivingtelephone in the distant earth branch will readily respond to their action the intermediate instruments will be totally irresponsive, for reasons hereinbefore stated.

In the drawings illustrating this specification, Figure 1 is a diagram of the plan I adopt Atem Aarranged in accordance with my invention. Fig. 3 shows di agrammatically the same coil 1 at station A, back to the point invention applied in multiple. Fig. 4 isa detail ofthe converting induction-coil, and Fig. 5 a detail of the magnetic core thereof.

In Fig. 1, Z represents a single metallic or double-wire telephone-circuit extending between two stations, A and B, w and w being the direct and return conductors thereof. At each station are two converting induction-coils, 1 and 2, the two insulating-wires of which (being preferably of substantially identical gage and length) are wound together, so that eachconductor is in close inductive proximityto the other throughout its entire length. One of the conductors, 30, of the converting-coils is included at each station, as shown, in the circuit of the direct wires w and i0', so that the said conductors of each coil are virtually placed in direct circuit serially with the said line. The lot-her conducting-wires, 3l, of the said coils are joined up in a local or homeeircuit comprising the receiving or magneto telephone t and the secondary helix of the transmittingtelephone induction coil T," the latter being operated in the usual manner through the intermediation of the primary helix by the transmitter 7 and battery 8. The local circuit may be traced as follows: wire 31 of converting-coil 1, secondary transmittercoil T, receiving-telephone t, wire 3l of converting-coil 2, and thence by conductor wL back to the starting-point. The route of the main circuit in like manner may be traced from an arbitrary starting-ponia@ at station A, through wire 30 of. converting-coil 2, line-wire w, through the converting-coils 1 and 2 at station B, and back ci@ lincwire w' and through Each converting-coil is provided with a soft-iron magnetic core, which is preferably adj ustable with respect to the extent of its inserwhereby when the nut is turned the screw, with IOO IIO

the magnetic .core attached thereto,is advanced -into or withdrawn from the interior of the helix. Y By using a micrometer or differential screw the adjustment may be effected withany requisite degree of tineness. y

lIn Fig. 2 I show a metallic or wire return'- practically equidistant from the two convert-` ing-coils 1 and 2, and passes through the regular telephone-instruments to earth at g. This earth-branchextension may of course be constructed of any convenient length extending to the stations G and H, which maybe located at a considerable distance from the points z and z. The telephone-instruments shown at each of these stations G and H consist in this case of a receiving-telephone, t, and a transmitter, 7, in a primary circuit including a battery, S, connected with the branch line w through its induction-coil 9. The instruments in both terminal branches are alike, and a description of one will thus serve for both. I have found in practice that stations A and B may freely and readily exchange oral comm unications without affecting the instruments at st-ations Gand H, and that G and H may in like manner communicate without interfering in any way with messages which may simultaneously bein course of transmission between A and B. Considering, rst, the case of the stations A and B. the secondary electrical. current generated in the secondary coils T of` the transmitters traverse the conductors 3l of the converting-coils l and 2, setting up corresponding induced currents therein, which eur# rents, being at any given moment of similar sign in the two coils l and 2, re enforce one another and pass over the line-wires w and wfto the distant station B, where,acting inductively through the converting-coilsl and 2,they affect the receiver t, reproducing the message transmitted at station A. rlhe two convertingcoils at the transinitti11g-station, whether A\' or B, may thus be unitedly regarded as the" source of undulatory electric energy for the double-wire circuit, and may be compared to two separate cells or sections of voltaic battery\ joined u'p serially, so as to re-enforce one another. They are therefore enabled to act cf"- feclively through the corresponding converting-coils in the metallic circuit at the distant station upon the receiver there, but have no effect upon the earth-branch receiver, because the currents originated in the metallic circuit (as a metallic circuit) continue to circulate therein without reference to the earth branches at eitherend of the double line. Considering, secondly/the case of messages transmitted from the instruments in the grouml-braneh stations G or H, any communication originating, for instance, at the station G will be transmitted by the instrument 7, and will of course initiate secondary currents in the coil 9. These voice-currents upon arriving at the j unction-point z divide, as indicated by the arrows, and proceedV partly upon the wire w and partly upon the wire fw to the distant station H. Arriving at the point e they reunite and affect the instruments included in the earth branch at station H, reproducing the original messages in the receiver t. The receivers at A and Bdo not rcspond to these voice-currents, because they pass through the wires 30 of the converting-coils ,l and 2 at both A and B with equal but opposite effect, the current induced in the wire Si. of l being opposite to thatinduced in the wire 31 of 2. The resultant effect, therefore, in the metallic circuit receivers is an absolute neutrality or nullity. This neutrality is, however, contingent upon the equality in resistance and inductive power of the corresponding converting-coils l and 2. Theyvmnst bc wound as nearly as possible with equal amounts of insulated wire of tne same gage, and an eX- act balance of inductive power is effected by varying the extent to which two magnetic cores, c, are inserted into their respective spools. l have found that by ordinary manual variation alone a substantial. balance can readily be effected. By adopting a screw-adjustment, using,preferably, a micrometer or di fferential screw, as in Fig. i, the balance can be brought with great ease to a perfect exactness; and I have also found that a most efciently-operating core can be made by rolling up soft sheet-iron into a circular form, as indicated in Fig. 5.

Fig. 3 shows the extension or elaboration of the principles involved. Two separate double-wire circuits, Z and Z', are employed, each corresponding in every feature to the circuit described as Z in Fig. 2. These are united at each end by a loop-wire, wf, provided on each of its arms with a converting-coil, 5 and 6. These coils bring into inductive relation to the line additional sets or stations of telephonie apparatus, E and F, and the wires t0 and w of the circuit Z serve together as one side of the line-circuit for these additional stations,while the wires w and w of the circuit Z serve in like manner unitedly for the other side of said line. Earth branches ai at both ends may again be attached to the electrical centers c and of both ofthe above described loops and contain the stations G and H. lt will be seen that this principle of connection is capable of indefinite expansion. At station B in Fig. 3 the adjustability ofthe converting-coil coresc is indicated by dotted lines.

Tay-stations may readily be connected with any of the double-wire circuits, as shown at J, the connections being arranged in precisely similar manner lto the terminal double-wire stations.

The usual signaling appliances are ofcourse in practice combined with the above system in a manner `well understood.

Having new described my invention, I Claim-e 1. rllhe combination, with a metallic or dou ble-wire main circuit, of local circuits at two or more stations located upon the said main circuit, t-he said local circuits including` telephone-instruments, and being connected with the main circuit by means of induction-coils, substantially as specified herein.

2. The combination, substantially as hereinbefore described, of a metallic or double-line main circuit and local telephone-circuits at the stations located upon the said main circuit, each of the said local circuits including TOO telephones, and being connected with the said rmain circuit by means of induction-coils, one

of the said coils being included in the outgoing and the other in the incoming line-wire of the said metallic circuit.

3. The combination, at a telephone-station,

of a metallic or doublewire main circuit, a local circuit, including telephones, and two in duction-coils, one wire of both of the said induction-coils being included in the said local circuit, and the other wre'of the'said coils being included one injeach line-wire of the double-wire circuit, as and for the purposes set forth. Y

4. The combination, in a system of. telephonic communication, of a metallic or dou ble parallellinc circuit extending between two or more stations, of local circuits, including telephone apparatus, connected by means of induction-coils with both sides of thesaid double-line main circuit, and earth branches, including telephones, connected with the said metallic circuits at the terminal stations thereof and at a point between the said ind`uctioncoils, whereby the stations inductively connected with the double-line circuit may be enabled to communicate with one another to the exclusion ofthe earth-branch stations, and vice versa, as hereinbefore described.

. 5. Inasystem oftelephonic communication, a metallic or double parallelline main circuit, a series of local circuits, each including telephones, induction-coils, two for each local circuit, connecting the said local circuits with both sides of the main circuit, one wire of each coil of a pair being included in the local circuit, and the remaining wire of the two coils being interposed, one in each line of the metallic circuit, and earth branch circuits, with telephones included therein, united to the said metallic circuits at the terminal stations thereof and at a pointsubstantiallyequidistant from both induction-coils, substantially as and for the purposes hereinbefore described.

6. TheA combination, substantially as hereinbefore described, of a main metallic or doubleline circuit, a series of local circuits, each including telephones, and each connected by means of inductioncoils with both sides of the double-line circuit, earth branches con- .nected with the said metallic circuit at the termini thereof and at a point thereof between the said induction-coils, and adjusting devices whereby the inductive power of the said coils may be varied, so that currents passing between the earth branches may be accurately balanced in the two inductione-coils,and so that their eii'ect upon the local-circuit receiving-instruments may be neutral.

7. The combination, in a system of telephonic communication, of a metallic or double parallel-line circuit, earth branches, including telephone apparatus, vconnected with the metallic circuit at both termini, a series of local circuits including telephones, and a pair of induction-coils for each local circuit, whereby the said local circuits are inductively'connected with both sides of the metallic circuit, as herein described,the said induction-coils having their two wires wound together being of approximately equal resistance and inductive power, Aand being provided with adjustable cores,

whereby communication may be individually maintained between the several local #circuit 4instruments and between the earth-branch in` struments, substantially as set forth. ,Y

In testimony whereof I have signed my name to this specification, in the presence of two subyscribing witnesses, this 17th day of J uly,` 1886.

JOHN A. BARRETT.

f `Witnesses:

Guo. WILLrs Pinnen, 'IHos. D. LocKwooD. 

